Embodiments described herein generally relate to downhole tools. More particularly, such embodiments relate to underreamers and expandable stabilizers for enlarging the diameter of a wellbore.
After a wellbore is drilled, an underreamer is oftentimes used to enlarge the diameter of the wellbore. The underreamer is run into the wellbore in an inactive state. In the inactive state, cutter blocks on the underreamer are folded inwardly toward the body of the underreamer such that the cutter blocks are positioned radially-inward from the surrounding casing or wellbore wall. Once the underreamer reaches the desired depth in the wellbore, the underreamer is actuated in to an active state. In the active state, the cutter blocks move radially-outward and into contact with the wellbore wall. The cutter blocks are then used to increase the diameter of the wellbore.
Conventional underreamers have cutter blocks with a fixed outer diameter when in the active state. As such, conventional underreamers are adapted to create a segment of the wellbore having an increased, but uniform, diameter. It is oftentimes desirable, however, for the wellbore to have varying diameters. For example, cutter blocks become worn down due to excessive vibration in the wellbore. Reducing the diameter of the cutter blocks tends to stabilize the downhole tool, thereby reducing or eliminating wear on the cutter blocks. Currently, this is achieved by pulling the underreamer out of the wellbore to the surface to adjust the outer diameter of the cutting blocks. This delay can lead to lost profits in the field.